A variety of phase change materials available are well known for their thermal characteristics in that during their phase change stage they can absorb or release the latent heat while the temperature of the material is kept constant. Textiles and other products incorporated with the phase change materials, especially in the microencapsulated forms, may establish a microclimate surrounding the modified goods in the temperature ranges of the melting points of the employed phase change materials (PCMs) and so may meet the requirement for comfort. The use of microencapsulated PCMs may be found in U.S. Pat Nos. 4,756,958 and 5,290,904.
U.S. Pat. Nos. 5,456,852 and 5,916,478 both describes processes of microcapsule manufacturing employing in situ polymerization, in which formaldehyde used may impose an environmental danger.
Examples of useful inherently flame retardant phase change materials may include halogenated paraffins having 10 to 22 carbon atoms and, more specifically, mono or poly-chlorinated and brominated paraffins such as bromooctadecane, bromopentadecane, bromononodecane, bromoeicosane, bromodocosane, and so on. Throughout the investigation of the present invention it is found that the micro-encapsulation of paraffin compounds is much more difficult than the relative processes for the other core materials mainly due to the unique characteristics of paraffin compounds. In particular, such PCMs have melting points in the region of 20 to 110° C. and solubility compatibility issues.
U.S. Pat. No. 6,077,597 to Pause teaches that an interactive thermal insulating system with three layers can be established. The first layer is a layer in high density comprising a substrate coated with a polymer binder in which a plurality of microspheres containing a phase change material are dispersed. The second layer is a low density fibrous mesh in which individual fibers contain a plurality of microspheres containing a phase change material dispersed therein. A third layer is a flexible substrate. The fibrous mesh is sandwiched between the coated layer and the third layer.
Although the above microencapsulation processes may be of great importance, they may still suffer from some drawbacks. The shell of the microcapsules as prepared in the above processes may be somewhat permeable especially when heated at high temperatures (for example at 130° C. and above) in a dry state, which may be necessary for fabrics coating in the curing stages. Further, residual formaldehyde in the emulsion may not be controlled effectively.